Breast density is a significant breast cancer risk factor assessed from mammograms. Due to measurement difficulties and the lack of automation, breast density is used mainly for research purposes and not for breast cancer risk purposes in the clinical environment.
The Breast Imaging Reporting and Data Reporting System (BI-RADS) lexicon includes a breast tissue description for x-ray mammography. This categorization is a four-state ordinal scale comprised of a compact description of the overall breast composition accompanied with a percentage fibroglandular (glandular) tissue estimation as defined in the lexicon: [1] the breast is almost entirely fatty (<25% glandular); [2] there are scattered fibroglandular densities (approximately 25%-50% glandular); [3] the breast tissue is heterogeneously dense, which could obscure detection of small masses (approximately 51%-75% glandular); and [4] the breast is extremely dense. This may lower the sensitivity of mammography (>75% glandular). As indicated, these were developed to assess the reading difficulty of mammograms with ascending score for the patient's report. These ratings are dictated by the radiologist and may vary. In epidemiologic research, this set of descriptors has been extended beyond its original purpose to include breast cancer risk assessments. However, there lacks an automated measure of breast density to facilitate the related clinical applications.